28. Signs shown in diagrams Nos. 419, 420 and 421 may be used only—
(a) in connection with a traffic census the taking of which on a road has been approved by the highway authority for that road, the Chief Officer of Police of the police area in which the road is situate and in writing by or on behalf of the Minister or the Secretary of State, as the case may be; and
(b) in the vicinity of the traffic census points appointed in writing by or on behalf of the Minister, or the Secretary of State, as the case may be.
29. Signs shown in diagrams Nos. 429 and 430 shall not be used in any County Borough , Borough or Urban District in England and Wales or in any Burgh in Scotland. Signs shown in diagrams Nos. 448 and 450 may be used only where the space available does not permit the use of signs shown in diagrams Nos. 431 to 433 inclusive, 437, 438 and 440, and only in County Boroughs, Boroughs or Urban Districts in England and Wales and Burghs in Scotland.
30. Signs shown in diagrams Nos. 449, 451, 453 , 454 and 480 may be used only at road junctions and signs shown in diagrams Nos. 452 and 479 shall be used only at approaches to road junctions. Signs shown in diagrams Nos. 479 and 480 shall only be used, and the sign shown in diagram No. 452 shall not be used, in County Boroughs, Boroughs or Urban Districts in England and Wales or in Burghs in Scotland.
31. Signs shown in the diagrams Nos. 449 and 456 may respectively be combined in use with signs shown in diagrams Nos. 451 and 457 and in either of such cases the remote route sign shall be placed vertically below the sign bearing the route symbol of the road on or near which the signs are placed.
32. Below the sign shown in either of the diagrams Nos. 487 and 488 there may be attached to the post on which the sign is mounted a notice containing conditions relating to the use of the parking place. The sign of the type shown in diagram No. 488 may be used only to indicate the location of a parking place on a road where the Chief Officer of Police of the police area in which the parking place is situate has consented in writing to the standing of vehicles without lights.
33. The sign shown in diagram No. 481 may be used only to indicate a parking place at a garage:—
(a) the entrance to which is not more than a quarter of a mile distant by road from the site at which the sign is erected; and
(b) the presence of which is not evident to users of the road in which the sign is erected either directly or by advertisement.
34. Signs of the types shown in diagrams Nos. 489 to 492 inclusive may be used only to regulate the movement of vehicles into and out of premises with more than one access to a road.
35. Carriageway markings as shown in diagram No. RM3 in the Second Schedule to the Regulations (hereinafter referred to as "the Second Schedule" ) may be placed on a road only where the surface of the road is unsuitable for the placing of a carriageway marking as shown in diagram No. RM2.
36. Studs incorporating reflectors may be placed on a road only if of a type the construction of which has first been approved in writing by or on behalf of the Minister or the Secretary of State, as the case may be.
